Cameco reveal Cigar Lake failures

09 May 2007

Cameco CEO, Gerry Grandey, has described the flood at the Cigar Lake uranium mine and the serious delays it has caused as a 'black eye' for the company. A spokesman said: "In the end, Cameco did not anticipate the geological structures encountered."

Grandey made his comments in a conference call, during which the causes of the flood identified by an independent investigation were disclosed.

Nine factors were identified, the most important of which relate to the rock fall near to the geologic unconformity, which actually holds the Cigar Lake uranium deposit. Cameco's primary goal in future would be to avoid the occurrence of any future water inflows in that area.

The company told World Nuclear News: "After reviewing the incident it was clear that we underestimated the risks involved in working in that particular area and the controls that were in place were not rigorously followed."

The rock fall occurred at the junction of two tunnels at which excavators has removed too much rock. A subsequent controlled explosion caused the rock fall and serious water inflow began.

LyleKrahn of Cameco explained that the tunnel was being developed in drybasement rock, above which there is significant water in the sandstone.The rock fall opened a path for the water to flow in. The company wasfreezing the ground in many areas to immobilize groundwater, but haddecided not freeze that area since it was dry and deemed to be lowerrisk. Although groundwater seepage is a normal feature of mines - particularly under geological conditions like those at Cigar Lake - Cameco have admitted that its 'many controls to address the risk' were not enough. Pumps could not expel the water quickly enough and bulkhead doors failed to seal off the area. Managers had to allow the entire mine to flood. No workers were hurt, but completion of the mine has been put back to 2010 from the original planned date of 2008. It will eventually produce 18 million pounds of U3O8 per year. The circumstances surrounding the rock fall point to a combination of design issues, insufficient assessment of the ongoing development, lack of quality control of the excavation and slow installation of ground support.

Krahn said the original mining plan specified the equipment that should be used to keep the tunnel excavation within specifications, but that this information was not properly communicated to the equipment operators.

Cameco's response document to the investogator's report says that the mine development process is inherently variable because of the variable nature of rock structures and strengths, combined with the imprecise nature of blasting.

"In the end, Cameco did not anticipate the geological structures encountered," said Krahn.